1. The electron impact spectra of acetone andacetone-d6 were measured and interpreted. The anomalously weak 7.4eV (59 700 cm-1) transition was demonstrated to arise from the forbidden X approaches limit of 3p(1A2) Rydberg Transition. 2. A resonant multiphoton ionization investigation of 1,4-cyclohexadiene confirmed the electron impact spectroscopic assignment of one optically allowed and one optionally forbidden p-Rydberg transition, thus confirmed the theoretical model of through bond interactions. 3. Through interpretation of the electronic spectra of a large number of conjugated poly enes, the supposedly low lying, forbidden (Ag) valence transition of all trans-polyenes was shown to be an allowed transition in the partially s-isomerized corresponding polyene.